While the integrated circuitry (IC) is evolving according to the Moore's Law, requirements on devices and system performance are becoming higher and higher. It has become increasingly important to integrate both passive devices and active devices on a same chip. With the development of SOC and RF circuits, many design companies and chip manufacturers are focusing on passive devices with a high integration degree, high accuracy, and high reliability, such as resistors.
Resistors integrated on a chip generally include buried layer resistors, well resistors, polysilicon resistors, and metal film resistors, etc. Among them, metal film resistors can be integrated in a backend of line process, without increasing the chip area, and, thus, their cost can be reduced. In addition, the temperature coefficient of resistance (TCR) of metal film resistors is small, so the influence of temperature on the resistance is small. Thus, the metal film resistors can provide resistance for circuits with high stability in an environment of different temperatures. In conventional technologies, metal film resistors can generally be manufactured using two-additional-lithography-mask techniques or one-additional-lithography-mask techniques.
FIG. 1 shows a metal film resistor made using two additional lithography masks according to the conventional techniques. As shown in FIG. 1, main process steps for making the metal film resistor structure 10 include: providing insulation layer 100 and forming lower copper interconnect 110 in insulation layer 100; forming diffusion barrier layer 120 above the lower copper interconnect 110 and the insulation layer 100 to protect against and block the copper diffusion of the lower copper interconnect 110; etching diffusion barrier layer 120 via photolithography using a first lithography mask to expose part of lower copper interconnect 110 without exposing the insulation layer 100; forming a metal film layer on the diffusion barrier layer 120 and the exposed copper interconnect 110; and etching the metal film layer via photolithography using a second lithography mask to form metal film resistor 130. Although this structure can control size and pattern of the metal film resistor, two additional lithography masks may be required and, thus, manufacturing cost may be greatly increased.
FIG. 2 shows a metal film resistor using one additional lithography mask according to the conventional techniques. As shown in FIG. 2, main process steps for making the metal film resistor structure 20 include: providing insulation layer 200 and forming lower copper interconnect 210 in the insulation layer 200; forming diffusion barrier layer 220 above the lower copper interconnect 210 and the insulation layer 200 to protect against and block the copper diffusion in the lower copper interconnect 210; forming a metal film layer on the diffusion barrier layer 220 without exposing either insulation layer 200 or lower copper interconnect 210; and etching the metal film layer via photolithography using a lithography mask to form metal film resistor 230. Of course, follow-up processes can also include forming an inter-metal dielectric layer (IMD) 240 and an upper copper interconnect 250 in the inter-metal dielectric layer 240, where the upper copper interconnect 250 and metal film resistor 230 are connected.
The second option only requires one additional lithography mask to integrate metal film resistor 230 into subsequent or back-end manufacturing processes, which may greatly reduce manufacturing cost. However, because the electrical connection of the metal film resistor 230 is through the upper copper interconnect 250, when etching the vias in the upper copper interconnect 250, over etching can damage the metal film resistor 230 or even completely etch away the metal film resistor 230 at the connection joint. Thus, the manufacturing process of the metal film resistor 230 may fluctuate substantially and may affect the performance of metal film resistor 230. Meanwhile, due to the etching issue, the metal film resistor 230 needs to maintain a substantial thickness. It is difficult to have very large square resistance value to satisfy the required large resistance (e.g., greater than 1000 Q/square) in certain analog and RF circuits. Thus, applications and development of such metal film resistors are limited.
The disclosed methods and systems are directed to solve one or more problems set forth above and other problems.